New York City, with approximately one-quarter of all IDU-related AIDS cases in the US, provides a unique opportunity for studying the epidemic of HIV/Aids among high-risk drug users. NDRI has conducted research on HIV and high-risk drug use since 1983. It currently has 9 funded projects focusing on this topic, and is thus ideally situated to house a Center for studying this epidemic. This proposal is for a P30 Center, to provide an infrastructure to these already funded projects, to increase the individual and synergistic research contributions made by the 9 projects. Five Cores are proposed to conduct the following activities: (1) provide data analysis and methodological support, including cross-project, trend and secondary data analyses, and development of new methodologies; (2) establish a community-based monitoring capability in a high prevalence NYC community to obtain ethnographic data on community factors influencing risk and to monitor trends in risk behaviors and HIV seroprevalence to inform NDRI's ongoing projects; (3) undertake strategic comparisons between the epidemic in NYC and other national and international communities, to permit community-level analyses of factors influencing seroprevalence, seroincidence, and risk behaviors; (4) training, and dissemination functions, including training personnel for the supported projects, and dissemination of findings to service providers, and (5) coordination and integration of resource to increase scientific interactions, support ongoing and new investigations, centralize common project functions, and mentor new investigators. The increased interaction, collaboration and synergy across NDRI investigators, projects and consultants as accomplished by these core functions, will enhance multidisciplinary research, increase the productivity of the investigators, make it possible to address new research questions, generate a synthesis and lead to increased impact and utilization of the resultant project conclusion and recommendations.